This invention relates to a method for the preparation of diphthalic anhydrides. The products are useful chemical intermediates for the further preparation of various compounds such as the corresponding tetra-carboxylic acids and the various derivatives thereof, including for example, the salts, esters, acyl halides, amides, imides and the like. The diphthalic anhydrides are particularly useful as monomers in the preparation of polyimides, for example by polycondensation with a suitable diamine, such as ethylenediamine or phenylenediamine.
Various methods for the preparation of diether diphthalic anhydrides have been described in the chemical literature. Earlier preparations were directed to the formation of the diether di-o-xylyl groups followed by oxidation to the diether diphthalic anhydride. See Koton et al, Zh. Org. Khim. 4, 774 (1968); and Zh. Org. Khim. 6, 88 (1970).
U.S. Pat. No. 3,965,125 to Myers teaches the preparation of halogenated phthalimides from halogenated phthalic anhydride and reaction of the phthalimide with an alkaline metal salt of a phenol or a diphenol to form the bis-ether imide which is then hydrolyzed, acidified, and dehydrated to the bis-ether phthalic anhydride.
Heath et al (U.S. Pat. No. 3,956,320) disclose the preparation of aromatic bis(ether anhydride) by reaction of a nitro-substituted phenyl dinitrile with a metal salt of a dihydroxy aryl compound in the absence of a dipolar aprotic solvent and conversion of the resultant aryl-oxy tetranitrile to the tetra-acid followed by dehydration to the aryloxy dianhydride. Thus, for example, the patentees disclose the reaction of hydroquinone with 4-nitrophthalolnitrile in the presence of potassium carbonate, followed by hydrolysis, acidification and dehydration to form the hydroquinone di-ether phthalic anhydride.
Johnson et al (U.S. Pat. No. 4,020,069) teach the reaction of a 4-nitro-N-alkyl phthalimide and an aromatic dihydroxy compound in the presence of potassium carbonate and dimethyl sulfoxide followed by hydrolysis to form a bis-ether dicarboxylic acid which may then be dehydrated to form the aromatic ether dianhydride.
U.S. Pat. No. 3,850,964 to Williams discloses a method for making aromatic bis(ether anhydrides) by reaction of alkali metal diphenoxides with halo or nitro-substituted aromatic anhydrides. Thus, for example, a sodium salt of 2,2-bis-(4-hydroxyphenyl)propane was reacted with 3-fluorophthalic anhydride in anhydrous dimethyl formamide to form 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride.
Markezich (U.S. Pat. No. 3,992,407) discloses the preparation of aromatic bisimides by reaction of a 3- or 4-fluoro-N-substituted phthalimide with an aromatic dihydroxy compound in the presence of a solid alkali metal fluoride, such as potassium fluoride, and using a dipolar aprotic compound as a solvent. Markezich discloses the preparation of aromatic bisimides by reaction of a 3- or 4-nitro-N-substituted phthalimide with an aromatic dihydroxy compound in the presence of a solid alkali metal fluoride in a dipolar aprotic solvent.